Organic friction material compositions currently used in clutch and brake linings of vehicles must be capable of withstanding severe operating temperatures and dynamic pressures experienced during repeated applications. To prevent a deterioration in performance and physical degradation during such applications, the linings are normally reinforced by asbestos fibers randomly dispersed throughout a resin matrix. However, recent medical evidence indicates that asbestos fibers can cause health hazards for people exposed thereto during the manufacture of clutch and brake linings. Unfortunately, because of the presence of fine diameter asbestos fiber during the manufacture of brake lining using asbestos fiber, a portion of the asbestos often becomes airborne in quantities that exceed the exposure standard of asbestos fiber in the United States as controlled by the Occupational Safety and Health Act of 1970.
In an effort to reduce the environment contamination by the asbestos fiber and thereby continue the manufacturing asbestos based organic friction linings, a water slurry process disclosed in U.S. patent application Ser. No. 754,477 has been evaluated. The water slurry can be transmitted throughout a manufacturing facility without contaminating the surrounding environment with asbestos fibers. However, before the friction material can be cured, the water in the slurry must be removed in order to be assured that any resulting lining has essentially the same operating characteristics as a lining made from a dry mix. Unfortunately, this process adds considerable cost to the manufacturing cost of a brake or clutch lining, and does not necessarily solve emission problems during finishing and inspection.
In an effort to use readily available materials and the same manufacturing facilities, as currently available, it has been suggested that glass and/or mineral fibers be used in place of at least a portion of the asbestos fillers. U.S. Pat. No. 3,967,037 discloses several lining compositions utilizing glass fiber in place of asbestos. From experimentation, it has been determined such lining compositions in normal operational conditions produce brake noise, severe rotor scoring and wear, and poor friction material life when the lining is mated with a cast-iron rotor or drum.